Alloy and method of making the same



Patented Jan. 15, 1929.

UNITED STATES PATENT OFFICE.

ASSIGNOB TO CHEST RFIELD m, 01' DETROIT, IICHIGAN, A OOBPORATIOR 01'IIOHIGLN.

2330! G. 131.1), 01' DETROIT, MICHIGAN,

IE'I'AI. G

ALLOY AND METHOD 0! m6 m sum Io Drawing. Application filed December 1,1984. Serial 10. 758,362.

This invention relates to alloys, more particularly those designed foruse in the production of high speed cutting tools.

This application is a continuation in part of my applications SerialNos. 463,033, filed April 20, 1921; 493,108, filed August 17,

1921, and 626,801, filed. March 22, 1923.

It is necessary that alloys for such purposes have the property of redhardness 10 so that a tool made therefrom may maintain its cutting edgeafter the same has become red hot.

In addition to heat resistance the alloy must also possess abrasivehardness and, for

this purpose, should contain embedded in the metallic matrix, hardcrystals, usually metallic carbides.

The principal object of this invention is to improve the matrix ofcarbide containing alloys of this character to increase their strengthand heat resistance and also reduce their liability to flake, crack orsplinter during use.

Other and further important objects of N the invention will hereinafterappear.

I have found that an alloy formed of hard carbides and a matrix composedof both cobalt and nickel as its basal components gives a much superiorcutting tool to one made with either cobalt or nickel al'one.

The metals of the chromium group form hard carbides which are suitablefor the present purpose although metals of other groups may also. beused if desired.

The metals of the chromium group comprise chromium, tungsten, molybdenumand uranium. While these metals show many resemblances to each other,both chemical and physical, they are far from being identical 1nproperties. The same is true of the somewhat closely allied metalsnickel and cobalt. To obtain the best results the individualcharacteristics of these metals should be blended, although theinvention is not restricted to the use of a plurality of metals of thechromium or other group. Thus chromium gives strength rather thanhardness as compared with tungsten. Then again, molybdenum will give asimilar hardening eflect to Further, alloys alone have a tendency to bewhile the cobalt alloys are Moreover, unless the quantit of nickel isroperly limited the product wfi not be satis actory especially asregards its heat resisting qualities.

The chief function of the cobalt and nickel appears to be that ofproducing a strong, tough, heat resisting matrix for the carbides of thechromium group or other group of metals. Neither cobalt or nickelpossesses the aflinity for carbon, that is possessed by chromium ortungsten for example, so that it is probable that there is little or nocarbide of either cobalt or nickel in my alloys.

The amount of carbon by weight in my alloys is comparatively slight, say1.50% but the proportion of carbide by volume may be as high as 20 to25% of the entire alloy. This follows from the great difierences inspecific gravity of carbon and the metals with which it combines to formcarbide. In view of this large content of nonmetallic compounds thecomposition of the matrix is of the utmost importance. It will also beevident that since these alloys may be regarded as a mass of carbidecrystals embedded in a strong, tough, heat resisting matrix, a varietyof carbides may be used with a matrix having as its basal constituentsboth cobalt and nickel.

ese carbides are soluble to a certain extent in the molten alloy so thatunless the carbon content exceeds certain limits depending upon thenature and proportion of the metals forming the alloy, the latter oncooling will not contain free carbide crys tals but only carbide insolid solution. While carbide in solid solution has a hardening effectit is not the desired abrasive hardness-which results from the presenceof free carbide crystals. The carbon content of the alloy should,therefore, be high enough to provide a substantial proportion of freecarbide crystals in the alloy.

Ordinarily, alloys made in accordance with this invention will consistof cobalt, nickel, chromium and tungsten with a small amount of carbon.

with nickel hot-short cold-short The percentage of these metals willusually be within the following limits:

Per cent. Cobalt 25 to 4:0 Nickel 10 to 20 Chromium 25 to 35 Tungst n 15to 35 The total amount of cobalt and nickel should be between 35 and65%.

In certain cases a wider range of proportions maybe employed such asthose lying with the following percentages:

Percent. Cobalt 10 to 45 Nickel 7 to 30 Chromium 20 to 45 Tungsten 10 to45 The total amount of cobalt and nickel should be between 30 and 70%.

As an example of a suitable alloy falling within the above limits thefollowing may be given:

Conversely if the cobalt is increased and the nickel is decreased asmaller proportion of chromium group metals are required. Thus:

Per cent. Cobalt 36 Nickel 10 Chromium 32 Tungsten 22 In some instancesonly one metal of the chromium group may be used, as in the case of thefollowing alloy:

Percent. Cobalt 45 Nickel a l5 Tungsten 4.0

In addition to the metallic constituents mentioned above a hardeningelement should be added. Usually this will be carbon although otherelements, more particularly silicon, have a. hardening effect. Manymetallic silicides are as hard if not harder than-the correspondingcarbides.

Usually the amount of carbon in the alloy eeasaa will be between 1 and2.5%, for example around 1.5% although in some cases it may be as low as0.5% or as high as 3.5%. It is desirable on the one hand to have enoughcarbon to produce free carbide cystals and."

on the other hand not enough to cause the formation of particles ofgraphitic carbon throughout the alloy, as the presence of graphiticcarbon greatly reduces the strength of the alloy.

As a given weight of chromium, for example, will combine with a muchlarger weight of carbon than will the same weight of tungsten the amountof carbon which may be added before free graphitic carbon is formed inthe alloy will depend upon the nature and proportions of the metalscomposing the alloy.

The carbon is most readily and accurately added as a carbide, such asthe carbide of one of the metals forming the alloy as chromium.

In addition to a hardening element it is frequently advisable to use ade-oxidizer such as aluminum or boron. Further the hardening element andde-oxidizer may to advantage be added simultaneously in the form ofboron carbide.

While my alloys consist essentially of the above metallic andnon-metallic ingredients it will be understood that the addition orpresence as impurities of small quantities of other metals, etc., suchas iron, manganese or the like, 7 will not change the generalcharacteristics of my alloys.

In the process of forming the alloy the several ingredients in properproportion are placed in a crucible preferably together with somereadily fusible material, such as glass, which will form a protectinglayer over the alloy and so prevent oxidation. Preferably the metals areplaced in the crucible in the order of their fusibilit-y and specificgravity.

Cobalt III. p 1490" C. Sp. gravity"- 8.72 N1cke1 m. p 1452 C. Sp.gravity 8.70 Chromium m. p 1505 C. Sp. gravity--- 6.92 Tungsten m. p.above 3060" C. Sp. gravity"- 18.70

The cobalt, nickel and chromium are placed at the bottom of the crucibleand then the tungsten placed on top so that when the first named metalsmelt the tungsten may sink by gravity through the molten mass and in sodoing be alloyed therewith.

The temperature employed for fusing the constituents may be from 1750 to1950 C. according to conditions. As these alloys do not respond to heattreatment, as does steel, at least at a temperature below 1100 C. thealloy must be formed into the desired shape by casting and then grindinginstead of by forging.

To obtain the best results molds made of sand should not be employedsince, using such molds, even if brushed over with graphite powder, thebars are apt to be full of blow holes and too soft to make good castingspecial sizes lathe tools. Preferably the molds are constructed ofgraphite althoug be used for this purpose if the surface 1s treatedbefore use to prevent the hot metal adhering thereto. Such treatment maycon sist eitherin treatment with sulphuric acid or coating with carbon asmoky flame thereto. 7

Graphite is, however, much superior to cast iron as a material formolds. In the first place it is much easier to machine graphite thancast iron so that molds for and shapes canbe more by the application ofreadily made. have to be repeatedly treated with sulphuric acid solutionsince the effect of the treatment soon wears otf.

Further, cast iron molds, especially for small sizes of bars, chills themetal too rapidly.- This chilling makes the bars hard, and, whilehardness is a desideratum, it should be uniform throughout the bar-andchilling makes the outer layers harder than the center.

Now graphite has a lower specific heat per unit volume and also a muchlower heat conductivity than cast iron. Consequently the rate ofabstraction of heat from the coolin metal is far less in the case ofgraphite than in the case of iron molds.

I have also found that the hardness of bars cast with the above alloysvary according to the rate at which they cool so that a small bar, whichnecessarily cools more rapidly than a large one, is, other conditionsbeing the same, harder. On the other hand, increasing the carbon contentof the alloy increases its harness. It has further been found that heattreatment of the alloy after casting does not appreciably change itshardness so that the alloy may be termed self-hardening.

To secure the best results it is necessary to hit the happy mean betweentoo great hardness, which means brittleness, and liability to flake orchip, and too little hardness, which means that a tool made therefromwill be too soft to cut for the desired length of time or to cut hardmetals.

This I accomplish by the present invention by varying the amout ofhardening element, such as boron carbide, added with varying dimensionsof the bar to be cast.

For example, for a inch bar 0.56% boron carbide may be used to advantae; for a inch bar 0.85%; and for a inch ar 0.97%.

By so varying the content of boron carbide the sum of the hardness dueto chilling and the hardness due to the hardening element is maintainedsubstantially uniform irrespective of the size of the bar cast.

If on casting a trial bar from any given melt the alloy appears to betoo soft, small Then again, cast iron molds additions of tungsten may beadded to the crucible to give the requisite hardness.

The above mentioned quantities of carbon, added as boron carbide, areconsiderably lower than the desired carbon contents or the bars for thereason that not only do the constituent commercial metals contain small.amounts of carbon but also larger amounts of carbon are picked up fromthe crucible in which the alloy is made, if an unlined graphite cruciblebe employed. I

As a result of the picking up of carbon from the crucible it isdesirable to avoid heating the metal to too high a temperature or fortoo long a time in the crucible. Further, when remelting scrap alongwith a proportion of new ,metal the quantity of boron carbide addedshould be decreased to allow for the carbon already in the scrap.

I am aware that the proportions of the constituents of the alloys andnumerous details of the method of manufacture of such alloys and toolstherefrom may be varied through a wide range without departing from thespirit of this invention, and I do not desire limiting the patentgranted, otherwise than as necessitated by the prior art,

I claim as my invention:

1. An alloy containing nickel and cobalt, not varying, jointly, widelyfrom 40 per cent of the total, each being present in substantial amount;chromium and tungsten, each not varying widely from 30 per cent of thetotal; and carbon, in appreciable amount.

2. An alloy containing nickel about 14 per cent, cobalt about 27 percent, chromium about 31 per cent, tungsten about 28 per cent and carbonabout 1.25 per cent.

3. An alloy in which nickel and cobalt constitute about 40 per cent,chromium and tungsten each about 30 per cent, and carbon about 1 percent.

4. A high speed tool composed essentially of 10 to 45% cobalt, 7 to 30%nickel, and 0.5 to 3.5% carbon, the remainder of the alloy consistingchiefly of a metal capable of forming a hard carbide.

5. An alloy comprising 10 to 45% cobalt, 7 to 30% nickel, and 0.5 to 35%carbon, the remainder of the alloy consisting chiefly of metal capableof forming hard carbide.

6. An alloy for high speed tools comprising 25 to 40% cobalt, 10 to 20%nickel, 25 to 35% chromium, 15 to 35% tungsten and 1.0 to 2.5% carbon.

7. The method of forming alloys of a. metal having the properties ofnickel or cobalt, chromium and tungsten comprising placing the firstmetal and chromium into the crucible as a lower layer, then placing thetungsten on top as an upper layer and heating the crucible to atemperature suflicient to melt the first metal and chromium and alloythe tungsten therewith. 8. A cast high speed tool of controlled hardnessand composed essentially of 10 to [B1 45% cobalt, 7 to 30% nickel, 0.5to 3.5% carbon and the remainder thereof being chiefly of a metalcapable of forming a hard carbide, the proportion of carbon varying(within the limlts set forth) propor- 10 tionally as the cross-sectionalarea of the tool.

9. A cast high speed tool of controlled hardness comprising 25 to 40%cobalt, 10 to 20% nickel, 25 to'35% chromium, 15 to 35% tungsten and 1.0to 2.5% carbon, the proportion of carbon being proportional within thelimits set forth to the cross sectional area of the tool.

In testimony whereof I have hereunto subscribed my name.

PERCY C. CHESTERFIELD.

